Conventionally, a linear solenoid is known to have a stator core having a tubular guiding portion, an attracting portion, and a blocking portion. The tubular guiding portion guides a plunger to move in an axial direction. The attracting portion attracts the plunger by generating a magnetic attractive force when a coil is energized. The blocking portion blocks a magnetic field between the guiding portion and the attracting portion. The guiding portion, the attracting portion, and the blocking portion are integrally coupled with each other to constitute the stator core. By integrally providing the guiding portion and the attracting portion, the guiding portion and the attracting portion can be more certainly provided coaxially, and a clearance between the plunger and the attracting portion in a radial direction can be smaller as much as possible.
In a linear solenoid described in Patent Document 1 (JP 2006-307984 A corresponding to US 2006/0243938 A1), a stator core has a thin portion provided by being recessed radial-inward, and the thin portion provides a blocking portion. Accordingly, the blocking portion can be thinner.
According to studies conducted by the inventors of the present disclosure, the linear solenoid of Patent Document 1 has a communication passage through which an interior space and an exterior space communicate with each other. When a plunger moves in an axial direction, a volume of the interior space is varied. By defining the communication passage, the linear solenoid adapts a variation of volume of the interior space. The communication passage is defined by a clearance between the stator core and a bottom of a yoke that has a bottomed-tubular shape and a clearance between a tubular portion of the yoke and a molding resin of a coil.
However, the communication passage communicates with a clearance defined between the stator core and a bobbin located inside of the coil. As a result, a foreign material such as metal powder may come from the exterior space into a recessed portion defined on an outer side of the blocking portion of the stator core. When magnetic particles such as the metal powder are accumulated at a bottom of the recessed portion, or when the magnetic particles are adhered to an inner wall of the bobbin to bridge the guiding portion and the attracting portion, a magnetic flux (i.e., a leakage flux) traveling between the guiding portion and the attracting portion while bypassing the plunger increases. Accordingly, magnetic attractive force of the stator core may decrease.